Selected Information About Buehler Corporation's Operations at High and at Low

Selected information about Buehler Corporation's operations at high and at low levels of activity follows: $$\begin{array} { | l | l | l | } \hline & { \text { Level of Activity } } \\\hline & \text { Low } & \text { High } \\\hline \text { Number of units produced } & 25,000 & 30,000 \\ \hline \text { Total manufacturing costs } & \$ 575,000 & \$ 680,000 \\\hline \text { Direct material cost per unit } & \$ 5 & \$ 5 \\\hline \text { Direct labour cost per unit } & \$ 6 & \$ 6 \\\hline\end{array}$$ Using the high-low method, what is the cost formula for manufacturing overhead?

A) $50,000 per period plus $22 per unit.
B) $50,000 per period plus $21 perD unit.
C) $50,000 per period plus $10 per unit.
D) $347,000 per period plus $0.10 per unit.